In the middle of the Cold War, the Soviet Union made great efforts to collect secret information through espionage. And the Il-20 showed to be a big breakthrough in this area. Even though only little information is known about the electronics and systems of the aircraft, it is believed that they were as capable as on the Boeing RC-135.
The aircraft was most frequently spotted over European waters, near Great Britain. The small box under the fuselage had a Side-Looking-Airborne-Radar (SLAR), for Radar and cartographic mapping in it, while the box on the side of the fuselage has a window for Infrared- and other optical sensors. Multiple antennas are used to collect data, two of them, which are mounted on the top of the fuselage, are used for satellite communication, allowing the Il-20 to transfer information to the ground crew in real time.